The present invention relates to an apparatus and method for uniformly applying a thin film of a lubricant to opposing surfaces of a plurality of substrates in a solventless manner. The invention has particular utility in the manufacture of magnetic or magneto-optical (xe2x80x9cMOxe2x80x9d) data/information storage and retrieval media comprising a layer stack or laminate of a plurality of layers formed on suitable substrates, e.g., disc-shaped substrates, wherein a thin lubricant topcoat is applied to the upper surface of the layer stack or laminate for improving tribological performance of the media when utilized with read/write transducers operating at very low flying heights.
Magnetic and MO media are widely employed in various applications, particularly in the computer industry for data/information storage and retrieval purposes. A magnetic medium in e.g., disc form, such as utilized in computer-related applications, comprises a non-magnetic disc-shaped substrate, e.g., of glass, ceramic, glass-ceramic composite, polymer, metal, or metal alloy, typically an aluminum (Al)-based alloy such as aluminum-magnesium (Alxe2x80x94Mg), having at least one major surface on which a layer stack or laminate comprising a plurality of thin film layers constituting the medium are sequentially deposited. Such layers may include, in sequence from the substrate deposition surface, a plating layer, e.g., of amorphous nickel-phosphorus (Nixe2x80x94P), a polycrystalline underlayer, typically of chromium (Cr) or a Cr-based alloy such as chromium-vanadium (Crxe2x80x94V), a magnetic layer, e.g., of a cobalt (Co)-based alloy, and a protective overcoat layer, typically of a carbon (C)-based material having good tribological properties. A similar situation exists with MO media, wherein a layer stack or laminate is formed on a substrate deposition surface, which layer stack or laminate comprises a reflective layer, typically of a metal or metal alloy, one or more rare-earth thermo-magnetic (RE-TM) alloy layers, one or more transparent dielectric layers, and a protective overcoat layer, for functioning as reflective, transparent, writing, writing assist, and read-out layers, etc.
Thin film magnetic and MO media in disc form, such as described supra, are typically lubricated with a thin film of a polymeric lubricant, e.g., a perfluoropolyether, to reduce wear of the disc when utilized with data/information recording and read-out heads/transducers operating at low flying heights, as in a hard disc system functioning in a contact start-stop (xe2x80x9cCSSxe2x80x9d) mode. Conventionally, a thin film of lubricant is applied to the disc surface(s) during manufacture by dipping into a bath containing a small amount of lubricant, e.g., less than about 1% by weight of a fluorine-containing polymer, dissolved in a suitable solvent, typically a perfluorocarbon, fluorohydrocarbon, or hydrofluoroether. However, a drawback inherent in such dipping process is the consumption of large quantities of solvent, resulting in increased manufacturing cost and concern with environmental hazards associated with the presence of toxic or otherwise potentially harmful solvent vapors in the workplace.
Another drawback associated with the conventional dipping method for applying a thin film of a polymeric lubricant to a substrate results from the lubricant materials being mixtures of long chain polymers, with a distribution of molecular weights. Since the molecular weight of the polymeric lubricant affects the mechanical (i.e., tribological) performance of the head-disc interface, it is common practice to subject the polymeric lubricant mixtures (as supplied by the manufacturer) to a fractionation process prior to adding the lubricant to the solvent in order to obtain a fraction having a desired molecular weight distribution providing optimal tribological performance. However, such pre-fractionation undesirably adds an additional step and increases the overall process cost.
Vapor deposition of thin film lubricants is an attractive alternative to dip lubrication in view of the above drawbacks. Specifically, vapor deposition of lubricant films is advantageous in that it is a solventless process and the process for generating the lubricant vapor can simultaneously serve for fractionating the lubricant mixture into a desired molecular weight distribution, thereby eliminating the need for a pre-fractionation step. Moreover, vapor deposition techniques can provide up to about 100% bonded lubricant molecules when utilized with appropriate polymeric lubricants and magnetic and/or MO disc substrates having deposition surfaces comprised of a freshly-deposited carbon-based protective overcoat layer which is not exposed to air prior to lubricant deposition thereon.
However, existing vapor deposition apparatus (e.g., the Intevac VLS 100 system, Intevac Corp., Santa Clara, Calif., described in detail in U.S. Pat. No. 6,183,831 B1, the disclosure of which is incorporated herein by reference) for applying a thin layer of polymeric lubricant to a thin film data/information storage and retrieval medium, e.g., in disc form, utilize a static process/system, wherein a single disc-shaped substrate is moved (e.g., by means of a disc lifter) to a position facing the orifices of a pair of oppositely facing lubricant vapor sources and statically maintained at that position while the lubricant film is deposited on the disc surfaces, with the lubricant film thickness being determined (i.e., controlled) by the length of the interval during which the disc surfaces are statically maintained facing the orifices of the lubricant vapor sources.
In order to control the spatial distribution, hence thickness uniformity, of the lubricant thin films obtained with such static vapor deposition process/apparatus at deposition rates of from about 1 to about 10 xc3x85/sec. for providing lubricant film thicknesses up to about 50 xc3x85, a diffuser plate for the lubricant vapor is provided intermediate the lubricant vapor source and the substrate surface, thereby adding to the system complexity and necessitating periodic maintenance of the diffuser plate for ensuring clear vapor passage through each of the openings in the diffuser plate. In addition, such static vapor lubrication systems incur a drawback when utilized as part of an in-line or similar type multi-chamber or modular system for manufacturing magnetic or MO media, in that a line-of-sight path is required for the mechanism utilized for positioning the disc surface opposite the lubricant vapor source. As a result, a path can be established for the lubricant vapor to escape from the lubricant deposition chamber into adjacent process chambers utilized for different processing functions and result in their being contaminated with lubricant vapor.
In addition to the above drawbacks, lubricant vapor deposition of disc substrates utilizing apparatus such as described in the aforementioned U.S. Pat. No. 6,183,831 B1 incurs several additional drawbacks and disadvantages, as follows:
while the process for generating the lubricant vapor can simultaneously serve for fractionating the lubricant mixture into a desired molecular weight distribution, thereby eliminating the need for a pre-fractionation step, when the finite amount of polymeric lubricant mixture initially contained in the vapor source is evaporated, the lighter, lower molecular weight (xe2x80x9cMWxe2x80x9d) molecules tend to evaporate first, leading to variation of the average MW of the deposited lubricant over time, which variation in turn results in a variation of the properties of the resultant lubricant films over time;
the single disc vapor deposition apparatus of U.S. Pat. No. 6,183,831 B1 typically forms part (i.e., a module) of a continuously operable, in-line apparatus for automated manufacture of magnetic or MO disc media, e.g., an Intevac MDP 250B Magnetic Disc Coater (as described in U.S. Pat. No. 5,215,420, the disclosure of which is incorporated herein by reference). However, combination of the single disc vapor deposition apparatus with the continuously operable, in-line apparatus for automated manufacture results in a significant reduction in product throughput, in that the latter apparatus is capable of processing approximately six times the number of discs that can be processed in a given period of time by the single disc vapor deposition apparatus of U.S. Pat. No. 6,183,831 B1;
the stream of lubricant vapor formed by the vapor sources in the apparatus of U.S. Pat. No. 6,183,831 B1 is circularly-shaped, and thus unable to provide a uniform thickness lubricant layer on a plurality of discs transported past the source on a conveyor means such as a pallet;
the lubricant vapor sources in the apparatus of U.S. Pat. No. 6,183,831 B1 lack provision for maintaining a constant distribution of lubricant MWs, inasmuch as the lubricant is evaporated from a reservoir within the respective sources which can only be manually replenished (i.e., filled), necessitating interrupting operation of the apparatus and opening of the chamber of the vapor lubricant module;
when, as indicated supra, the vapor deposition apparatus of U.S. Pat. No. 6,183,831 B1 forms part (i.e., a module) of a continuously operable, in-line apparatus for automated manufacture of magnetic or MO disc media (e.g., an Intevac MDP 250B Magnetic Disc Coater), operation of the vapor deposition module or portion of the system entails removing discs from a cassette which holds up to 25 freshly carbon-coated discs unexposed to air, and vapor lubricant coating the discs one-at-a-time. Because the first disc removed from the cassette for vapor lubrication is always colder than the last, due to its shorter residence time in the vapor lubrication main chamber prior to being subjected to lubricant vapor deposition thereon, the resultant lubricant coating on the first disc is thicker than that formed on the last disc. Further, since discs at the ends of the cassette radiate heat to different surfaces than interiorly-located discs, they also attain different temperatures prior to lubricant deposition thereon and therefore exhibit corresponding variations in lubricant coating thickness; and
the apparatus of U.S. Pat. No. 6,183,831 B1 does not provide for removal of lubricant from the cassettes prior to their re-insertion into the apparatus for re-use.
In view of the above, there exists a clear need for improved means and methodology for depositing thin films of a lubricant, e.g., a polymeric lubricant, by vapor techniques and at deposition rates consistent with the throughput requirements of automated manufacturing processing, e.g., of magnetic and/or MO data/information storage and retrieval media, which means and methodology overcome the above-described drawbacks and disadvantages of the conventional static lubricant vapor deposition technology. More specifically, there exists a need for improved means and methodology for vapor depositing thin films of lubricant (e.g., a polymeric lubricant) which provides improved lubricant film thickness uniformity over the entire deposition area of disc-shaped substrates utilized in the manufacture of such magnetic and/or MO media.
The present invention addresses and solves problems and difficulties in achieving uniform thickness lubricant thin film deposition over a plurality of disc-shaped substrates by means of vapor deposition techniques, e.g., thin film polymeric lubricant deposition on disc substrates utilized in the manufacture of magnetic and/or MO media, while maintaining full capability with all aspects of conventional automated manufacturing technology therefor. Further, the means and methodology afforded by the present invention enjoy diverse utility in the manufacture of various other devices and articles requiring deposition of uniform thickness thin film lubricant layers thereon.
An advantage of the present invention is an improved pass-by method for simultaneously vapor depositing a uniform thickness thin film of a lubricant on at least one surface of each of a plurality of substrates.
Another advantage of the present invention is an improved pass-by method for simultaneously vapor depositing a uniform thickness thin film of a lubricant on at least one surface of each of a plurality of substrates as part of an in-line process for the manufacture of disc-shaped magnetic and/or magneto-optical recording media.
Yet another advantage of the present invention is an improved apparatus for performing simultaneous pass-by vapor deposition of a uniform thickness thin film of a lubricant on at least one surface of each of a plurality of substrates.
Still another advantage of the present invention is an improved apparatus for performing simultaneous pass-by vapor deposition of a uniform thickness thin film of a lubricant on at least one surface of each of a plurality of substrates as part of an in-line process/apparatus utilized for the manufacture of disc-shaped magnetic and/or magneto-optical (MO) recording media.
Additional advantages and other aspects and features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to an aspect of the present invention, the foregoing and other advantages are obtained in part by a pass-by method for simultaneously vapor depositing a uniform thickness thin film of a lubricant on at least one surface of each of a plurality of substrates, comprising steps of:
(a) providing an in-line apparatus comprising:
(i) a chamber having an interior space maintained at a reduced pressure below atmospheric pressure, the chamber including entrance and exit means at opposite ends thereof;
(ii) at least one linearly extending vapor source means for supplying the interior space of the chamber with at least one linearly extending stream of lubricant vapor;
(iii) a substrate/workpiece mounting/supporting means for mounting/supporting thereon a plurality of substrates/workpieces with the surfaces thereof in facing relation to said at least one linearly extending vapor source means; and
(iv) a transporter/conveyor means for continuously moving the substrate/workpiece mounting/supporting means transversely past the at least one stream of lubricant vapor from the at least one linearly extending vapor source means;
(b) introducing a substrate/workpiece mounting/supporting means into the chamber via the entrance means, the substrate/workpiece mounting/supporting means supporting thereon a plurality of substrates/workpieces with similar thermal histories;
(c) continuously moving the substrate/workpiece mounting/supporting means with the plurality of substrates/workpieces mounted/supported thereon transversely past the at least one linearly extending stream of lubricant vapor from the at least one linearly extending vapor source means and depositing a uniform thickness thin film of the lubricant on at least one surface of each of the plurality of substrates/workpieces; and
(d) withdrawing the substrate/workpiece mounting/supporting means with the plurality of lubricant thin film-coated substrates/workpieces mounted/supported thereon from the chamber via the exit means.
According to certain embodiments of the present invention, step (a) comprises providing an in-line vapor deposition apparatus comprising at least one spaced-apart, opposed pair of said linearly extending vapor sources for supplying the interior space of the chamber with at least one pair of opposingly directed, linearly extending streams of lubricant vapor for depositing a uniform thickness thin film of the lubricant on opposing surfaces of each of the plurality of substrates/workpieces; and the substrate/workpiece mounting/supporting means (iii) and the transporter/conveyor means (iv) are adapted for continuously moving the plurality of substrates/workpieces transversely past the pair of linearly extending vapor sources.
In accordance with particular embodiments of the present invention, step (a) comprises providing an in-line vapor deposition apparatus comprising at least one spaced-apart, opposed pair of vertically oriented, linearly extending vapor sources for supplying the interior space of the chamber with at least one pair of opposingly directed, linearly extending, vertically oriented streams of lubricant vapor; and the substrate/workpiece mounting/supporting means (iii) and the transporter/conveyor means (iv) are adapted for continuously moving a vertically oriented plurality of substrates/workpieces transversely past the pair of vertically oriented, linearly extending vapor sources.
According to embodiments of the present invention, step (b) comprises introducing into the chamber a substrate/workpiece mounting/supporting means mounting/supporting thereon a plurality of disc-shaped substrates for magnetic or magneto-optical (MO) recording media, each having a pair of opposed major surfaces with a stack of layers constituting the magnetic or MO media formed thereon, each layer stack including an outermost, freshly coated carbon-containing protective overcoat layer, wherein step (b) further comprises introducing the plurality of substrates into the chamber such that the freshly coated carbon-containing protective overcoat layer is not exposed to the atmosphere.
In accordance with embodiments of the present invention, step (a)(ii) comprises providing at least one linearly extending vapor source means for supplying at least one linearly extending stream of a vaporized polymeric fluorine-containing lubricant material, and step (a)(ii) further comprises providing a vapor source means including a plurality of reservoirs of liquid polymeric fluorine-containing lubricant material, wherein the liquid polymeric lubricant material comprises a range of molecular weights and the plurality of reservoirs contain different volumes of liquid lubricant material for regulating the molecular weight distribution of the at least one stream of lubricant vapor for minimizing variation of the thickness of the thin films of lubricant during an interval in which the method is performed.
According to particular embodiments of the present invention, step (a)(ii) comprises providing the at least one vapor source means as fabricated of a high thermal conductivity material and including a plurality of linearly arranged vapor orifices for supplying the at least one linearly extending stream of lubricant vapor.
In accordance with a preferable embodiment of the present invention, step (a)(iii) comprises providing the substrate/workpiece mounting/supporting means in the form of a flat planar pallet including a plurality of spaced-apart openings extending therethrough, each of said openings including means for releasably mounting/supporting therein a flat planar substrate/workpiece.
According to further embodiments of the present invention, the method further comprises the step of:
(e) cleaning the substrate/workpiece mounting/supporting means subsequent to performing step (d) and prior to performing step (b) with another plurality of substrates/workpieces supported thereon.
In accordance with still other embodiments of the present invention, step (a) further comprises providing the in-line vapor deposition apparatus as part of a continuously operable, in-line apparatus adapted for performing at least one antecedent processing step and/or at least one subsequent processing step on the plurality of substrates/workpieces carried by the substrate/workpiece mounting/supporting means.
Another aspect of the present invention is an apparatus for performing simultaneous pass-by vapor deposition of a uniform thickness thin film of a lubricant on at least one surface of each of a plurality of substrates, comprising:
(a) chamber means having an interior space adapted to be maintained at a reduced pressure below atmospheric pressure, the chamber means including entrance and exit means at opposite ends thereof;
(b) at least one linearly extending vapor source means for supplying the interior space of the chamber with at least one linearly extending stream of lubricant vapor;
(c) a substrate/workpiece mounting/supporting means adapted for mounting/supporting thereon a plurality of substrates/workpieces with the surfaces thereof in facing relation to the at least one linearly extending vapor source means, each of the substrates/workpieces having a similar thermal history; and
(d) a transporter/conveyor means for continuously moving the substrate/workpiece mounting/supporting means transversely past the at least one linearly extending stream of lubricant vapor from the at least one linearly extending vapor source means for depositing a uniform thickness thin film of lubricant on the surfaces of each of a plurality of substrates/workpieces facing the at least one linearly extending vapor source means.
According to embodiments of the present invention, the at least one linearly extending vapor source means (b) comprises at least one spaced-apart, opposed pair of linearly extending vapor sources for supplying the interior space of the chamber (a) with at least one pair of opposingly directed, linearly extending streams of lubricant vapor for depositing a uniform thickness thin film of the lubricant on opposing surfaces of each of the plurality of substrates/workpieces; and the substrate/workpiece mounting/supporting means (c) and the transporter/conveyor means (d) are adapted for continuously moving the plurality of substrates/workpieces transversely past the linearly extending streams of lubricant vapor from the pair of linearly extending vapor sources.
According to a particular embodiment of the present invention, the at least one spaced-apart, opposed pair of linearly extending vapor sources are oriented vertically for supplying the interior space of the chamber with at least one pair of opposingly directed, linearly extending, vertically oriented streams of lubricant vapor; and the substrate/workpiece mounting/supporting means (c) and the transporter/conveyor means (d) are adapted for continuously moving a vertically oriented plurality of disc-shaped substrates/workpieces transversely past the pair of vertically oriented, linearly extending vapor sources.
In accordance with embodiments of the present invention, the vapor source means (b) comprises a high thermal conductivity material and includes a plurality of linearly arranged vapor orifices for supplying the at least one linearly extending stream of lubricant vapor; and the vapor source means (b) includes a plurality of reservoirs each adapted to contain a quantity of liquid polymeric lubricant material, wherein the liquid polymeric lubricant material comprises a range of molecular weights and the plurality of reservoirs are adapted to contain different volumes of liquid lubricant material for regulating the molecular weight distribution of the stream of lubricant vapor for minimizing variation of the thickness of the thin films of lubricant during an interval of operation of the apparatus.
According to certain embodiments of the present invention, the substrate/workpiece mounting/supporting means comprises a flat planar pallet including a plurality of spaced-apart openings extending therethrough, each of the openings including means for releasably mounting/supporting therein a flat planar substrate/workpiece.
In accordance with further embodiments of the present invention, the chamber means (a) has a cross-sectional area sufficiently large to eliminate difference in lubricant vapor pressure along the length of the at least one linearly extending vapor source means (b), whereby the vapor source means (b) delivers a uniform flow of lubricant vapor along its length; and the chamber means (a) includes means for monitoring the rate of vapor effusion from the at least one linearly extending vapor source (b).
According to still other embodiments of the present invention, the apparatus further comprises:
(e) cleaning means for cleaning the substrate/workpiece mounting/supporting means (c) subsequent to withdrawal from the chamber means (a) via the exit means and prior to re-introduction to the chamber means (a) via the entrance means.
According to another aspect of the present invention, the pass-by vapor deposition apparatus forms part of a continuously operable, in-line apparatus adapted for performing at least one antecedent processing step and/or at least one subsequent processing step on said plurality of substrates/workpieces carries by the substrate/workpiece mounting/supporting means.
Yet another aspect of the present invention is an apparatus for performing simultaneous pass-by vapor deposition of a thin film of a lubricant on at least one surface of each of a plurality of substrates, comprising:
(a) chamber means having an interior space adapted to be maintained at a reduced pressure below atmospheric pressure, the chamber means including entrance and exit means at opposite ends thereof; and
(b) means within the chamber for performing pass-by vapor deposition of a uniform thickness of the thin film of lubricant on at least one surface of each of the plurality of substrates.
Additional advantages and aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present invention are shown and described, simply by illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as limitative.